1. Field of the Invention
The invention relates to a braking device for safety belts, especially safety belts for motor vehicles, which have a locking device arranged ahead of it, and in which a belt brake becomes activated by the belt pull.
2. Description of the Prior Art
In safety belt systems, after the locking of the belt in an automatic roll-up device, there are approximately 50 to 100 mm of belt band which can still be pulled out from the belt portion rolled up in the automatic roll-up device, due to a film-spool effect at the roller. By sequentially arranging a holding device which arrests the belt after a short path, that is, almost immediately, this undesired film-spool effect is avoided.
There are devices known (GB No. 1,416,517) provided with such belt braking provisions, in which, when the belt brake is activated, the belt band is mechanically pressed between suitably shaped clamping jaws and thereby prevented from being pulled out any further. During this clamping, the fabric of the belt is strongly squeezed in small local areas and thereby damaged, so that the belt is unable with the required safety factor to accept the forces imposed by a crash. This unreliability factor is further aggravated by the fact that this clamping action occurs not only at an accident, but also during sharp braking when the belt brake is activated and moves into the clamping position. Severe damage to the belt results from the repeated clamping actions during its normal lifetime. The danger exists under these conditions that the belt will break in the case of an accident, a fact proven by suitable experiments. Therefore, in practice, these known belt-braking devices were not used.
Furthermore, braking devices for safety belts have been disclosed (for example, German Published Non-Prosecuted Application No. 19 49 061), wherein an energy-absorbing element is so constructed that a non-stretch belt is conducted around several shafts or rollers with a smooth surface, so that high friction forces are created, but the belt web is not damaged. In this manner, one obtains a certain degree of braking; however, this method cannot effect the complete blocking of the belt-roll-off. For this purpose, a great number of rollers would have to be arranged in series, and this would result in an unacceptable size and height of the device, and also causes deterioration of the belt due to the wear caused by the multiple deflections.